Re: Does v7.2.x support AIX 5.1?

Zeugswetter Andreas SB SD wrote:
>
> > > I don't have AIX 5 here, so cannot test, sorry.
> > > But yes, it should definitely work.
> > >
> > > There is a known possible performance improvement for concurrent sessions on
> > > multiprocessor AIX machines. The now depricated "cs(3)" used for the AIX TAS
> > > implementation should be replaced with fetch_and_or, compare_and_swap or the
> > > like. I just haven't got round to doing a patch that I trust.
> > >
> > > Maybe Tatsuo can say more ?
> >
> > cs() is gone in 7.3beta because cs() was failing on SMP machines anyway.
> > The new code is:
> >
> > #define TAS(lock) _check_lock(lock, 0, 1)
> > #define S_UNLOCK(lock) _clear_lock(lock, 0)
>
> Ah, great. That is perfect. Has slipped in without me noticing :-)

According to CVS, it was Tomoyuki Niijima:

---------------------------------------------------------------------------

I tried to build PostgreSQL with the following step to see backends hung
during the regression test. The problem has been reproduced on two machine
but both of these are the same type of hardware and software. I also tried
to recreate the problem on other machines, on older version of AIX but I
couldn't.

After looked through pgsql-hackers mailing list, I focused on spin lock
issue to solve the problem. The easiest and may not be the best solution
for the problem is to give up HAS_TEST_AND_SET. This actually works.

One another and better solution for the problem is to use _check_lock() and
_clear_lock() as spin lock. Important thing here is to define S_UNLOCK()
with _clear_lock(). This will solve the so called "Compiler bug" issue
someone wrote on the mailing list.

We have some other API such as cs(), compare_and_swap() and fetch_and_or()
to do test and set on AIX, but any of these didn't solve my problem. I
wrote tiny testing program to see if we have any bug of these API of AIX,
but I couldn't see any problem except for compare_and_swap(). It seems that
you can not use compare_and_swap() for the purpose, as it would not work as
spin lock on any SMP machines I tested. I don't know the reason why cs()
nor fetch_and_or()/fetch_and_and() will not work with PostgreSQL on p690.
These worked with my testing program on all machines I tested.

--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073